1 files changed, 215 insertions, 0 deletions
diff --git a/models/db/list.go b/models/db/list.go
new file mode 100644
index 0000000..5c005a0
--- /dev/null
+++ b/models/db/list.go
@@ -0,0 +1,215 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package db
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"xorm.io/builder"
+	"xorm.io/xorm"
+)
+
+const (
+	// DefaultMaxInSize represents default variables number on IN () in SQL
+	DefaultMaxInSize     = 50
+	defaultFindSliceSize = 10
+)
+
+// Paginator is the base for different ListOptions types
+type Paginator interface {
+	GetSkipTake() (skip, take int)
+	IsListAll() bool
+}
+
+// SetSessionPagination sets pagination for a database session
+func SetSessionPagination(sess Engine, p Paginator) *xorm.Session {
+	skip, take := p.GetSkipTake()
+
+	return sess.Limit(take, skip)
+}
+
+// ListOptions options to paginate results
+type ListOptions struct {
+	PageSize int
+	Page     int  // start from 1
+	ListAll  bool // if true, then PageSize and Page will not be taken
+}
+
+var ListOptionsAll = ListOptions{ListAll: true}
+
+var (
+	_ Paginator   = &ListOptions{}
+	_ FindOptions = ListOptions{}
+)
+
+// GetSkipTake returns the skip and take values
+func (opts *ListOptions) GetSkipTake() (skip, take int) {
+	opts.SetDefaultValues()
+	return (opts.Page - 1) * opts.PageSize, opts.PageSize
+}
+
+func (opts ListOptions) GetPage() int {
+	return opts.Page
+}
+
+func (opts ListOptions) GetPageSize() int {
+	return opts.PageSize
+}
+
+// IsListAll indicates PageSize and Page will be ignored
+func (opts ListOptions) IsListAll() bool {
+	return opts.ListAll
+}
+
+// SetDefaultValues sets default values
+func (opts *ListOptions) SetDefaultValues() {
+	if opts.PageSize <= 0 {
+		opts.PageSize = setting.API.DefaultPagingNum
+	}
+	if opts.PageSize > setting.API.MaxResponseItems {
+		opts.PageSize = setting.API.MaxResponseItems
+	}
+	if opts.Page <= 0 {
+		opts.Page = 1
+	}
+}
+
+func (opts ListOptions) ToConds() builder.Cond {
+	return builder.NewCond()
+}
+
+// AbsoluteListOptions absolute options to paginate results
+type AbsoluteListOptions struct {
+	skip int
+	take int
+}
+
+var _ Paginator = &AbsoluteListOptions{}
+
+// NewAbsoluteListOptions creates a list option with applied limits
+func NewAbsoluteListOptions(skip, take int) *AbsoluteListOptions {
+	if skip < 0 {
+		skip = 0
+	}
+	if take <= 0 {
+		take = setting.API.DefaultPagingNum
+	}
+	if take > setting.API.MaxResponseItems {
+		take = setting.API.MaxResponseItems
+	}
+	return &AbsoluteListOptions{skip, take}
+}
+
+// IsListAll will always return false
+func (opts *AbsoluteListOptions) IsListAll() bool {
+	return false
+}
+
+// GetSkipTake returns the skip and take values
+func (opts *AbsoluteListOptions) GetSkipTake() (skip, take int) {
+	return opts.skip, opts.take
+}
+
+// FindOptions represents a find options
+type FindOptions interface {
+	GetPage() int
+	GetPageSize() int
+	IsListAll() bool
+	ToConds() builder.Cond
+}
+
+type JoinFunc func(sess Engine) error
+
+type FindOptionsJoin interface {
+	ToJoins() []JoinFunc
+}
+
+type FindOptionsOrder interface {
+	ToOrders() string
+}
+
+// Find represents a common find function which accept an options interface
+func Find[T any](ctx context.Context, opts FindOptions) ([]*T, error) {
+	sess := GetEngine(ctx).Where(opts.ToConds())
+
+	if joinOpt, ok := opts.(FindOptionsJoin); ok {
+		for _, joinFunc := range joinOpt.ToJoins() {
+			if err := joinFunc(sess); err != nil {
+				return nil, err
+			}
+		}
+	}
+	if orderOpt, ok := opts.(FindOptionsOrder); ok {
+		if order := orderOpt.ToOrders(); order != "" {
+			sess.OrderBy(order)
+		}
+	}
+
+	page, pageSize := opts.GetPage(), opts.GetPageSize()
+	if !opts.IsListAll() && pageSize > 0 {
+		if page == 0 {
+			page = 1
+		}
+		sess.Limit(pageSize, (page-1)*pageSize)
+	}
+
+	findPageSize := defaultFindSliceSize
+	if pageSize > 0 {
+		findPageSize = pageSize
+	}
+	objects := make([]*T, 0, findPageSize)
+	if err := sess.Find(&objects); err != nil {
+		return nil, err
+	}
+	return objects, nil
+}
+
+// Count represents a common count function which accept an options interface
+func Count[T any](ctx context.Context, opts FindOptions) (int64, error) {
+	sess := GetEngine(ctx).Where(opts.ToConds())
+	if joinOpt, ok := opts.(FindOptionsJoin); ok {
+		for _, joinFunc := range joinOpt.ToJoins() {
+			if err := joinFunc(sess); err != nil {
+				return 0, err
+			}
+		}
+	}
+
+	var object T
+	return sess.Count(&object)
+}
+
+// FindAndCount represents a common findandcount function which accept an options interface
+func FindAndCount[T any](ctx context.Context, opts FindOptions) ([]*T, int64, error) {
+	sess := GetEngine(ctx).Where(opts.ToConds())
+	page, pageSize := opts.GetPage(), opts.GetPageSize()
+	if !opts.IsListAll() && pageSize > 0 && page >= 1 {
+		sess.Limit(pageSize, (page-1)*pageSize)
+	}
+	if joinOpt, ok := opts.(FindOptionsJoin); ok {
+		for _, joinFunc := range joinOpt.ToJoins() {
+			if err := joinFunc(sess); err != nil {
+				return nil, 0, err
+			}
+		}
+	}
+	if orderOpt, ok := opts.(FindOptionsOrder); ok {
+		if order := orderOpt.ToOrders(); order != "" {
+			sess.OrderBy(order)
+		}
+	}
+
+	findPageSize := defaultFindSliceSize
+	if pageSize > 0 {
+		findPageSize = pageSize
+	}
+	objects := make([]*T, 0, findPageSize)
+	cnt, err := sess.FindAndCount(&objects)
+	if err != nil {
+		return nil, 0, err
+	}
+	return objects, cnt, nil
+}